Confinement effects in PbSe quantum wells and nanocrystals

The effect of quantum confinement in PbSe quantum wells and dots is studied using tight binding calculations. Compared to zinc-blende semiconductors, unusual physical properties are predicted for rock salt PbSe nanostructures. The energy gap increases as the inverse of the size both for wells and dots. For PbSe nanocrystals, the luminescence lifetime, the confinement energy, and the intraband optical properties are in good agreement with experiments. The high quantum yield observed experimentally can be explained by the absence of surface dangling bonds in these systems. The origin of the second peak measured in the absorption spectra is discussed, whereas S-P interband transitions exhibit very small oscillator strength. The full frequency-dependent dielectric function epsilon(omega) is calculated for PbSe quantum wells. Its imaginary part epsilon(2)(omega) is strongly anisotropic and shows large variations with respect to its bulk value even far from the gap region.